We have 100+ tests failing now that our main testing sandbox has received the 2020 release. We can no longer deploy. We're getting many errors like
Unexpected error: You have uncommitted work pending
And custom errors such as
Failed to make request
implying that our tests are making http callouts, and not being mocked properly. These tests were previously passing without any org changes. What in the 2020 release could cause this behavior?
We are unable to find a minimum test case because running the whole test suite fails, but running individually failing tests pass.
Running tests in serial with Apex Test execution > Click Options > Disable Parallel Apex Testing has no effect
edit: this breaking change confirmed by other users
In testing Summer '20 in our sandboxes, there was an uptick in test failures around callouts.
We see some callout failures with message "System.CalloutException: You have uncommitted work pending. Please commit or rollback before calling out"
edit community report confirms https://success.salesforce.com/issues_view?id=a1p3A000000ATF1QAO
edit another bug report to signal boost https://success.salesforce.com/issues_view?id=a1p3A0000003UWIQA2